The present invention relates to a semiconductor light-emitting device and a flat panel display lighting system using the semiconductor light-emitting device. More particularly, the semiconductor light-emitting device is usable as, for example, a backlighting source that irradiates a liquid crystal display with light through a light guide plate.
A display that utilizes a liquid crystal has been generally applied to electronic devices such as cellular phones. The display using the liquid crystal has a structure in which the liquid crystal display is sealed with the liquid crystal and a light emitter such as a light-emitting diode (LED) is used as a backlighting source to display an image. A semiconductor light-emitting device of edge-lighting type, for example, is known as a light-emitting device used as the backlighting source.
FIGS. 7(a) through 7(c) are respectively perspective view of a semiconductor light-emitting device used for a flat panel display lighting system of edge-lit type, side view and front view, of the flat panel display lighting system.
As shown in FIG. 7(a), a known semiconductor light-emitting device includes: blocklike insulating substrate 50; pair of electrodes 51a and 51b, each of which is disposed to cover each end of the front face (i.e., the face on which a light emitter is placed), a side face and the back face (which is opposite to the face on which the light emitter is placed), of the substrate 50; light emitter 52 bonded onto the electrode 51a with a conductive adhesive; wire 53, which electrically connects the electrode 51b to the light emitter 52; and resin package 54, which is made of an epoxy resin and molds, for example, the light emitter 52 and wire 53 together on the front face of the substrate 50.
As shown in FIGS. 7(b) and 7(c), the known flat panel display lighting system includes a board 55 on which the semiconductor light-emitting device and a light guide plate 56 of a polymer such as an acrylic polymer are disposed. The semiconductor light-emitting device is mounted on the board 55 and used as a backlighting source for a liquid crystal display 57. The board 55 has a wiring pattern (not shown) for establishing continuity to the electrodes 51a and 51b of the semiconductor light-emitting device. The light guide plate 56 is used for guiding light, emitted from the light emitter 52, to the liquid crystal display 57 and has a minute unevenness pattern on its bottom surface. Because of the existence of this minute unevenness pattern, light introduced into the edge of the light guide plate 56 is externally reflected toward the liquid crystal display 57. That is to say, light generated by the light emitter 52 of the semiconductor light-emitting device is introduced into the edge of the light guide plate 56. In other words, the light guide plate 56 is edge-lit. Thus, the light guide plate 56 functions as a backlighting source for the liquid crystal display 57 utilizing the light diffusion therein.
In such a surface-mounted flat panel display lighting system, the semiconductor light-emitting device is fixed onto the board 55 so as to be electrically connected to the electrode 51a and 51b and the wiring pattern using solders 58a and 58b. In this case, the height of the semiconductor light-emitting device is determined by the height (i.e., the vertical length shown in FIG. 7(a)) of the substrate 50. Specifically, the height of the light emitter 52 is set to be almost a half of that of the substrate 50.
The substrate 50, however, has been diced so as to have a height and a thickness enough to retain the mechanical strength thereof. Therefore, the light emitter 52 is limited in height when mounted on the board 55. Thus, the thickness of the light guide plate 56 also needs to be set in accordance with the height of the light emitter 52. That is to say, to introduce light into almost the center of the edge face of the light guide plate 56, the light guide plate 56 needs to have its thickness increased or to be mounted slightly apart from the upper surface of the board 55. Accordingly, an unit made up of the flat panel display lighting system and liquid crystal display 57 has its thickness increased. As a result, the unit is less applicable to electronic devices such as cellular phones that have been tremendously downsized and thinned. In addition, the board 55 also has a space for the substrate 50, and thus has its area as well as its thickness increased inevitably. Therefore, it becomes difficult to downsize the resultant device.
Though not shown in FIGS. 7(b) and 7(c), circuits such as drive and detector circuits for the light emitter 52 are formed on the lower surface of the board 55. Thus, a solder reflow process step is required for such circuits on the lower surface of the board 55. Moreover, as an example shown in FIGS. 7(b) and 7(c), if the light emitter 52 is mounted on the upper surface of the board 55 and fixed thereto with solders 58a and 58b, another solder reflow process step is required on the upper surface of the board 55. Consequently, fabrication of the flat panel display lighting system includes two solder reflow process steps on the respective upper and lower surfaces of the board 55. As a result, the number of process steps and items of control inspection increase, and thus increase in fabricating cost and decrease in production yield might eventually occur.
It is therefore an object of the present invention to have a structure for backlighting a liquid crystal display downsized and thinned. It is another object of the present invention to provide a semiconductor light-emitting device and a flat panel display lighting system of high productivity by reducing, for example, the number of the fabricating process steps.
An inventive semiconductor light-emitting device includes: a substrate having a base portion, which extends laterally, and a mounting portion, which extends longitudinally from an area located in a middle part of the base portion and has an element placing area in a position apart from the base portion; a pair of electrodes formed on the base portion and the mounting portion of the substrate, one of the pair of electrodes extending from an end of the base portion, the other of the pair of electrodes extending from the other end of the base portion; a light emitter, which is placed on the electrode placing area of the mounting portion and is electrically connected to each of the pair of electrodes; and a transparent encapsulant, which molds at least the light emitter and each part of the pair of electrodes together.
In this device, the light emitter is disposed in an area of the mounting portion located away from the base portion of the substrate, and light emitted from the light emitter can be taken out from the area. Therefore, light emission suitable for application can be obtained. Specifically, the known semiconductor light-emitting device needs to be mounted on a board with its upper surface attached to the board by vacuuming using, for example, a vacuum jig. Thus, the area in the board where the device is attached using a suction nozzle is limited in position and the board itself is also limited to a minimum dimension. Further, since the substrate of the semiconductor light-emitting device is limited in thickness, the resin package is also limited in size and shape and the light emitter is also limited in location, for example. As a result, there is little flexibility in designing, and thus emission characteristics have to be sacrificed to some extent. In contrast, the inventive semiconductor light-emitting device can be mounted through the board with the lower surface of the base portion attached to the board by vacuuming using a vacuuming jig. Thus, the inventive semiconductor light-emitting device does not have limitations such as those found in the known semiconductor light-emitting device. As a result, flexibility in designing a shape of the resin package and a height of the light emitter increases, and more desirable emission characteristics can be obtained.
In addition, the mounting portion of the semiconductor light-emitting device can be made smaller than the overall substrate of the known semiconductor light-emitting device. Therefore, if a board through which a semiconductor light-emitting device is mounted has an adequate structure, the entire system can be downsized.
An inventive flat panel display lighting system includes: a board including a circuit pattern; an opening formed from the upper surface through the lower surface of the board in a region of the board other than a region on which the circuit pattern is formed; a light guide plate mounted over the upper surface of the board in a region other than the opening of the board; and a semiconductor light-emitting device including a substrate, which has a base portion extending laterally and a mounting portion extending longitudinally from an area located in a middle part of the base portion and having an element placing area in a position apart from the base portion, a pair of electrodes formed on the base portion and the mounting portion of the substrate, one of the pair of electrodes extending from an end of the base portion, the other of the pair of electrodes extending from the other end of the base portion, a light emitter, which is placed on the electrode placing area of the mounting portion and is electrically connected to each of the pair of electrodes, and a transparent encapsulant, which molds at least the light emitter and each part of the pair of electrodes together. The light emitter molded in the encapsulant faces a face of the light guide plate. Each of the pair of electrodes is electrically connected to the circuit pattern of the board.
In this system, since the height from the upper surface of the board to the top of the light emitter can be set lower than that of the known system, the thickness of the unit made up of the light guide plate and the board can be reduced. As a result, the flat panel display lighting system can be thinned. In addition, the upper surface of the board is not occupied by the semiconductor light-emitting device other than in the opening through which the mounted portion, molded with the encapsulant of the semiconductor light-emitting system, is set. As a result, the area of the upper surface of the board occupied by the semiconductor light-emitting device is reduced, thus downsizing the overall flat panel display lighting system.
In one embodiment of the present invention, the circuit pattern of the board may be formed on the lower surface of the board. Each of the pair of electrodes of the semiconductor light-emitting device may be formed on the upper surface of the board of the semiconductor light-emitting device. Each of the pair of electrodes of the semiconductor light-emitting device may be in contact with a part of the circuit pattern formed on the lower surface of the board and may be electrically connected to the circuit pattern. Then, a solder reflow process performed only on the lower surface of the board is enough to fabricate the flat panel display lighting system. As a result, the number of fabricating process steps decreases, thus reducing fabricating cost and increasing production yield.